The present invention relates to rotary pumps, compressors, and blowers, and particularly to blowers of the Roots type. More particularly, the present invention relates to pumps and blowers of the type having rotors non-rotatably attached to their shafts, such as by press-fitting or some other suitable means.
Although the present invention may be used with various types of pumps and blowers, it is especially advantageous when used with a Roots type blower, and will be described in connection therewith.
Rotary blowers of the Roots type typically include a pair of meshed, lobed rotors, with each of the rotors being mounted on a shaft, and each shaft having mounted thereon a timing gear. Rotary blowers, and particularly Roots blowers, which are employed as superchargers for internal combustion engines normally operate at relatively high speeds, typically in the range of 10,000 to 20,000 rpm.
As is well known to those skilled in the art, it is preferable that the rotors mesh with each other, to transfer volumes of air from an inlet port to an outlet port, without the rotors actually touching each other, although it is known to permit certain types of coated rotors to have limited contact. It is now becoming more common to utilize some sort of clutch (typically, electrically operated) disposed between an input pulley and the blower, in order to be able to disengage the blower when its operation is not required. The durability and life of such a clutch, as it engages and disengages the blower, is determined largely by the inertia of the rotors which, in turn, is a function of the size and mass (weight) of the rotor lobes. Typical Roots blowers produced commercially by the assignee of the present invention for use as internal combustion engine superchargers have a lobe radius in the range of about 2 inches (about 5 cm) to about 3 inches (about 7.5 cm).
The desire to reduce the rotating mass, and therefore the inertia, of the rotor lobes has caused those working in the art to attempt to develop rotors which do not have solid lobes, i.e., at least some portion of each lobe is "hollow". In some of the so-called "hollow" rotor designs, the "hollow" portion would be in communication with some portion of the pressurized air, thus creating a leakage path reducing volumetric efficiency. In other attempts at producing hollow lobed rotors, the hollow portion of each lobe was wholly within the lobe, and therefore would not result in a leakage path. However, such rotors were typically of a two-piece type of construction, requiring the addition of either an "endcap" to enclose the hollow chamber, or some sort of plug arrangement. In either case, one result was the need for subsequent, additional machining operations on the rotor, thus making the rotor economically unacceptable.